package com.example.demo.config;
public class Thread1 extends Thread{
public void run() {
System.out.println("Thread-1: try get lock A...");
synchronized (Demo.lockA) { //给A加锁
System.out.println("Thread-1: lock A got.");
Demo.sleep1s();
System.out.println("Thread-1: try get lock B...");
synchronized (Demo.lockB) {//获取B锁
System.out.println("Thread-1: lock B got.");
Demo.sleep1s();
}
System.out.println("Thread-1: lock B released.");
}
System.out.println("Thread-1: lock A released.");
}
}
package com.example.demo.config;
public class Thread2 extends Thread{
public void run() {
System.out.println("Thread-2: try get lock B...");
synchronized (Demo.lockB) {//给B加锁
System.out.println("Thread-2: lock B got.");
Demo.sleep1s();
System.out.println("Thread-2: try get lock A...");
synchronized (Demo.lockA) {//获取A锁
System.out.println("Thread-2: lock A got.");
Demo.sleep1s();
}
System.out.println("Thread-2: lock A released.");
}
System.out.println("Thread-2: lock B released.");
}
}
package com.example.demo.config;
public class Demo {
static final Object lockA = new Object();
static final Object lockB = new Object();
private Integer value=0;
private Integer another=0;
public Integer getValue() {
return value;
}
public void setValue(Integer value) {
this.value = value;
}
public Integer getAnother() {
return another;
}
public void setAnother(Integer another) {
this.another = another;
}
public void add(int m) {
synchronized (lockA) { // 获得lockA的锁
System.out.println("获得lockA的锁0");
this.value += m;
synchronized (lockB) { // 获得lockB的锁
System.out.println("获得lockB的锁0");
this.another += m;
} // 释放lockB的锁
} // 释放lockA的锁
}
public void dec(int m) {
synchronized (lockB) { // 获得lockB的锁
System.out.println("获得lockB的锁1");
this.another -= m;
synchronized (lockA) { // 获得lockA的锁
System.out.println("获得lockA的锁1");
this.value -= m;
} // 释放lockA的锁
} // 释放lockB的锁
}
static void sleep1s() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
new Thread1().start();
new Thread2().start();
Demo demo=new Demo();
try {
demo.add(2);
demo.dec(2);
} catch (Exception e) {
e.printStackTrace();
}
}
}
结果:
Connected to the target VM, address: '127.0.0.1:51315', transport: 'socket'
Thread-1: try get lock A...
Thread-2: try get lock B...
Thread-2: lock B got.
Thread-1: lock A got.
Thread-1: try get lock B...
Thread-2: try get lock A...
造成死锁,
线程1 A加锁后获取B
线程2 B加锁后获取A
造成线程1获取B锁进入等待
线程2获取A锁进入等待,死循环下取
思维没有好的解决办法,只有停止虚拟机进行解决